Here's how I think the game works when it comes to image processing especially the ranks.
Since all the rank images are set in the same file it uses a sprite
technique. So if your change the indexes of the images you will end up with half pics or complete blanks because the game is only set to read a certain co-ords of the grade image.
This being said there should be a somewhere, I think killstatus.sdata, where these co-ordinates and their corresponding the rank count is stored. What you would have to do is edit say killstatus.sdata or wherever the data is stored and edit the ranks. I am currently trying the find the data structure of killstatus.sdata, if I get it I'll post it here.
btw...The ranks names are stored in sysmsg-uni.
Can you show me where you got the extended rank list. It might help move things faster.